The plan is directed to identification of a test or tests which can distinguish the asymptomatic carrier of AIDS from healthy controls. It is assumed that AIDS can be transmitted by an infectious agent during the asymptomatic incubation period or in a chronic healthy carrier state. The tests will be evaluated in populations with a high probability of including asymptomatic carriers: (1) blood donors to patients who developed AIDS, (2) recipients of blood from donors who develop AIDS, and (3) 1,000 prospectively followed homesexually-active males, of which 30 to 60 will probably develop AIDS during the study. Appropriate controls will be studied in the same way. Serologic tests to be evaluated include thymosin alpha-1, thymosin beta-4, beta-2 microglobulin, acid-labile alpha interferon, tests for HTLV, anti-HBc and anti-CMV, as well as others which become available later. HLA typing will be done on a selected group for evidence of genetic susceptibility. New approaches to detecting asymptomatic carriers of AIDS will be developed from flow cytometry studies using not only standard reagents but also new monoclonal antibodies identifying other mononuclear subpopulations. Simultaneous two-color fluorescent cytometry will permit identification of subpopulations with markers which may be associated with AIDS. If successful, the tests can be used to identify asymptomatic carriers of AIDS, prevent their dissemination of the disease by inappropriate contacts or blood donation, and indicate high-risk subjects who should be observed closely for evidence of AIDS.